Electric motor controls



March 15, 1966 ...25- HOIST F LOWER Filed July 10, 1961 INVENTOR S.

HARRY M. COOK CHRISTIAN CHERMELY United States Patent 3,241,022 ELECTRIC MOTOR CONTROLS Harry M. Cook, Cleveland, and Christian Chermely, Wicklitfe, Ohio, assignors to The Clark Controller Company, Cleveland, Ohio, a corporation of Ohio Filed July 10, 1961, Ser. No. 122,817 7 Claims. (Cl. 318-261) Our invention relates to electric motor controls and more particularly to a system for controlling an electric motor when used to drive a hoist and the like.

Heretofore, electric control systems of this type did not rapidly stop and hold the load after it was hoisted through the position of the overhoist limit switch, providing the drum controller was left in some of the hoist positions. The contacts of the overhoist limit switch, when tripped, disconnected the motor from the source and reconnected it in a dynamic braking circuit. Also, once stopped, the load was allowed to lower out of the limit switch due to its own weight. This was because the limit switch contacts did not disconnect the winding of the friction brake from the source of power. As soon as the load lowered out of the limit switch, the limit switch contacts operated to reconnect the motor to the source; and since the drum controller remained in the hoist position, the load would again hoist through the limit switch. This cycling of the load in and out of the limit switch was dangerous and, in addition, caused undue wear on the equipment.

It is therefore an object of our invention to provide a hoist control system which prevents the cycling of the load through the overhoist limit switch.

It is a further object of our invention to require that the drum controller be moved to the off position to reset the control system after the load has hoisted through the overhoist limit switch.

It is another object of our invention to provide a hoist system which prevents the speed of lowering out of the overhoist limit switch from becoming excessive.

It is still a further object of our invention to provide a protective circuit for a hoist system which is insensitive to momentary voltage surges and yet which is very sensitive to sustained voltage signals.

It is still another object of our invention to provide a hoist scheme wherein the cycling is prevented and the motor shunt connection can be utilized in the hoisting direction.

It is still another object of our invention to prevent the motor from running away should the overhoist limit switch fail to reset when lowering the load.

The embodiment of our invention utilizes a voltage relay having a time delay that is connected across the series field winding when the overhoist limit switch is not tripped and connected across the dynamic braking resistor when the overhoist limit switch is tripped. This relay has a contact in the control circuit of the hoist system, whereby should the voltage across either the series field winding or the dynamic braking exceed that required to operate the relay for a predetermined time interval, the relay operates to de-energize the control circuit. Deenergization of the control circuit disconnects power from the motor and from the brake so that the brake sets to stop and hold the motor. The relay is provided with a time delay so it will be insensitive to normal transient voltages and yet extremely sensitive to the proper voltage signals.

Operation of the relay requires that the control circuit be reset by moving the drum controller to the off position and thereby re-establishing the energizing circuit for the control circuit.

Other objects and advantages of our invention will become apparent to those skilled in the art when the follow- Patented Mar. 15, 1966 ing description is read in conjunction with the single figure drawing.

Referring to the drawing, there is shown at 10 an armature of a DC. motor having a series field winding 11.

Armature 10 is connected to be energized from a source of DC. power represented by wires 12 and 13 through contacts of various contactors. When contactors M and H are operated to close contacts M1 and H1, armature 10 is energized to rotate in the hoisting direction. When contactors M and L are operated to close contacts M1 and L1, armature 10 is energized to rotate in the lowering direction.

Armature 10 is connected by a drive shaft 14 to a hoist drum 15 which has a cable 16 wound thereon. At the free end of cable 16 is a load hook 17 which serves as the means to engage the load to be hoisted or lowered. Hook 17 has an arm 18 which serves to engage and operate an overhoist limit switch when hook 17 is hoisted too high. The overhoist limit switch is diagrammatically represented at 19 and has normally open contacts 20 and 21 and normally closed contacts 22 and 23.

Armature 10 is also connected to a normally set friction brake (not shown) of known construction, having an electromagnetic winding 24 for releasing the friction brake when energized. When winding 24 is not energized, the friction brake sets to stop rotation of armature 10 and drum 15.

At 25 generally is a drum type controller which, in the diagrammatic illustration thereof, comprises movable contacts 26 to 36. Contacts 27 through 36 are all connected together as shown and connected through contact UV1 and wire 37 to wire 12. Contact 26 is connected directly by wire 37 to wire 12 and will only conduct current when drum controller 25 is in its off position.

These contacts, as will be understood by those skilled in the art, are all movable in unison from the illustrated 01f position towards the right to five successive lowering points La to L2, or towards the left to five successive hoisting points Ha to He, indicated by the vertical lines below the legends LOWERING and HOISTING.

On the several lowering points, movable contacts 27 and 28 and 30 to 36 are engageable with bar contacts 38 to 46; and on the several hoisting points, movable contacts 27 to 29 and 32 to 36 are engageable with bar contacts 47 to 54.

Drum controller 25, on the various described points, operates or restores electromagnetic contactors as follows.

A contactor UV having a winding and normally open contacts UV1 and UV2.

A contactor M having a winding 56 and a normally open contact M1.

A contactor 5A having a winding 57 and a normally open contact 5A1 and a normally closed contact 5A2.

A contactor H having a winding 58 and normally open contacts'Hl and H2 and a normally closed contact H3.

A contactor L having a winding 59 and normally open contacts L1 and L2 and a normally closed contact L3.

A contactor 1A having a winding 60 and a normally open contact 1A1 and a normally closed contact 1A2.

A contactor S having a winding 61 and normally open contacts S1 to S3 and a normally closed contact S4.

A contactor CR having a winding 62 and a normally open contact CR1 and normally closed contacts CR2 and CR3.

A contactor DB having a winding 63 and a normally open contact DB1 and normally closed contacts DB2 and DB3.

A contactor 2A having a winding 64 and normally open contacts 2A1 and 2A2 and a normally closed contact 2A3.

A timing contactor 2T having a winding 65 and a normally closed contact 2T1.

A timing contactor 1T having a winding 66 and a normally open contact 1T1 and a normally closed contact 1T2.

A timing contactor 3T having a Winding 67 and normally open contacts 3T1 and 3T2.

A contactor 3A having a winding 68 and normally open contacts 3A1 and 3A2 and a normally closed contact 3A3.

A contactor 4A having a winding 69 and normally open contacts 4A1 and 4A2 and a normally closed contact 4A3.

Timing contactors 1T, 2T and 3T are of the known type that have means delaying their contact operation until a time interval has elapsed after energization of their windings.

The contactors and timing contactors are all illustrated in normally de-energized or restored condition. The said contacts of these contactors and timing contactors are shown without connections thereto, but are reproduced elsewhere in the drawing, with their connections, to thereby avoid complexity in the drawing.

The windings of the contactors are shown in an acrossthe-line type of diagram comprising horizontal wires 70 to 80, with their left ends connected to bar contacts of drum controller 25. The right end of wire 70 is connected to wire 13. The right end of wires 71 to 76 are connected to a wire 81. The right end of wires 77 to 80 are connected to a wire 82.

In the illustrated off position of drum controller 25, contactor UV is operated by current through controller contact 26, cross wire 70, winding 55 of contactor UV and contactor XVRl to wire 13. Contactor UV operates to close contact UV1 which connects wire 12 by wire 37 directly to contacts 27 through 36. Contact UV2 closes to connect wire 81 to wire 13. The control circuit is now connected to the source and ready for operation.

On the first point of hoisting Ha, contactor M is operated by current through contact 27, bar contact 47, cross wire 7-1, winding 56, wire 81, contact UV2 to wire 13. Contactor M operates to close contact M1.

At the same time, contactor H is operated by current from contact 29, through bar contact 49, cross wire 73, contact 54, winding 58 of contactor H, Wire 81 and contact UV2 to wire 13. Contactor H operates to close contacts H1 and H2 and open contact H3.

The operation of contactors M and H connect the motor so that it is energized by current flowing from wire 12 through contact H1, con-tact 22, armature 10, contact 23, series field 11, winding 24, resistor sections R1, R2, R3 and R4, and contact M1 to wire 13. Resistor sections R5 and R6 and contact DB2 are connected in parallel with contact 22, armature 10, contact 23 and series field 11.

The current flowing through winding 24 of the friction brake releases the brake, allowing the motor to rotate. Armature 10 is energized with current in a direction to cause the motor to rotate in the hoisting direction, but at a low hoisting speed due to the series connected resistors R 1 to R4- and the armature shunt circuit of resistors R5 and R6.

On going to the second point of hoisting Hb, the operating conditions described for the first hoisting point remain the same; and additionally, contactor 5A operates to short out resistance section R2 and contactor DB operates to open the armature shunt circuit as follows.

Current flows through controller contact 28, bar contact 48, cross wire 72, contact 2T1, winding 57 of contactor 5A, wire 81 and contact UV2 to Wire 13. Contactor 5A operates to close contact 5A1 which shorts out resistance section R2, and contact 5A2 opens.

Controller contact 32 engages the bar contact 50 and current flows therethrough and through contact H2, cross wire 76, winding 63 of contactor DB, contact DB3, wire 81 and con-tact UV2 to wire 13. Contactor DB operates to close contact DB1 and open contacts DB2 and DB3.

The opening of contact DB2 disconnects the armature shun-t circuit consisting of resistors R5 and R6. The opening of contact DB3 inserts resistor R7 in the energizing circuit of winding 63. The closing of contact DB1 connects wire 82 to Wire 13.

The motor is now energized by current from wire 12 through contact H1, cont-act 22, armature 10, contact 23, series field 11, winding 24, resistor R1, contact 5A1, resistor R3, resistor R4, and contact M1 to wire 13. Armature 10 is now energized with a higher current and is caused to hoist the load at a faster speed.

On going to the third point of hoisting He, the oper ating conditions described for the second hoisting point remain the same; and additionally, contactor 2A operates to connect resistors R8, R9 and R10 in parallel with resistors R1 and R3 which is accomplished as follows.

Controller contact 33 engages with bar contact 51 and current flows therethrough and through cross wire 77, contact L3, winding 64 of contactor 2A, wire 82 and contact DB1 to Wire 13. Contactor 2A operates to close contacts 2A1 and 2A2 and open contact 2A3. The closing of contact 2A1 connects resistors R8, R9 and R10 in parallel with resistors R1 and R3.

The closing of contact 2A2 allows current to flow from controller contact 34 through bar contact 52, contact 2A2, cross wire 78, winding 66 of timing contactor 1T, wire 82 and contact DB1 to wire 13. After the elapse of a time interval, contactor 1T operates to close contact 1T1 and open open contact 1T2.

The motor is now energized by current from wire 12 through contact H1, contact 22, armature 10, contact 23, series field 11, winding 24, the parallel connected resistors R1 and R3, and R8, R9 and R10, resistor R4, and contact M1 to wire 13. The armature 10 is now energized with increased current so the motor rotates to hoist the load at a higher speed.

On going .to the fourth point of hoisting Hd, the operating conditions described for the third hoisting point remain the same; and additionally, contactor 3A operates to short out resistor R10 as follows.

Controller contact engages with bar contact 53 and current flows therethrough and through cross wire 79, contact 1A2, contact 1T1, winding 68 of contactor 3A, wire 82 and contact DB1 to wire 13. It is to be noted, that winding 68 cannot be energized until after the expiration of the time interval of timing contactor 1T. After this expires, contactor 3A is operated to close contacts 3A1 and 3A2 and open contact 3A3. The closing of contact 3A1 shorts out resistor R10 to connect resistors R1, R3 and R4 in parallel with resistors R8 and R9.

The closing of contact 3A2 allows winding 67 of contactor 3T .to be energized through the circuit consisting of controller contact 34, bar contact 52, cross wire 78, contact 3A2, winding 67, Wire 82 and contact DB1 to wire 13. After the expiration of its time interval, contacts 3T1 and 3T2 operate to close.

Current now flows through the motor from wire 12 to contact H1, contact 22, armature 10, contact 23, series field 11, winding 24, the parallel circuit of resistors R1, R3 and R4 and contacts M1 with resistors R8 and R9 to wire 13. The motor is energized with a still higher current to cause it to hoist the load faster.

On going to the fifth point of hoisting He, the operating conditions described for the fourth hoisting point remain the same; and additionally, contactor 4A operates to remove all of the resistance from the armature circuit as follows.

Controller contact 36 engages with bar contact 54 and current flows therethrough and through cross Wire 80, contact 3T2, winding 69 of contactor 4A, wire 82 and contact DB1 to wire 13. Contactor 4A cannot operate until after the elapse of the time interval for timing contactor 3T, after the expiration of which, contactor 4A operates to close contacts 4A1 and 4A2 and open,

contact 4A3. The closing of contact 4A1 shorts out the remaining resistor sections from the motor circuit.

The motor is now energized by current flowing from wire 12 through contact H1, contact 22, armature 10, contact 23, series field 11, winding 24, contact 2A1, and contact 4A1 to wire 13. The motor is now energized with its maximum current and will therefore hoist the load at the maximum speed.

On going to the first point of lowering La, contactors M, L and 5A are operated as follows.

Controller contact 27 engages with bar contact 38 and current flows therethrough and through cross wire 71, winding 56 of contactor M, wire 81 and contact UV2 to wire 13.

Controller contact 28 engages with bar contact 39 and current flows therethrough and through cross wire 72, contact 2T1, winding 57 of contactor 5A, wire 81 and contact UV2 .to wire 13.

Controller contact 30 engages with bar contact 40 and current flows therethrough and through cross wire 74, contact 2A3, winding 59 of contactor L, wire 81 and contact UV2 to wire 13.

Also, current fiows from controller contact 30 through bar contact 40, cross wire 74, contact 2A3, contact 1T2,

winding 60 of contactor 1A, wire 81 and contact UV2 to wire 13. Contactor 1A operates to close contact 1A1 and open contact 1A2.

The motor is now connected to be energized as a shunt motor by current flowing from wire 12 through contact L1, the circuit of armature 10, contact 22, resistors R5 and R6, and contact DB2, connected in parallel with contact 23 and series field 11, and thence through winding 24 and resistor R1, and resistor R3 which is parallel connected with resistors R9 and R10, resistor R4 and contact M1 to wire 13.

On going to the second point of lowering Lb, the operating conditions described for the first lowering point remain the same; and additionally, contactors S, and DB are energized to continue to operate the motor as a shunt motor as follows.

Controller contact 31 engages bar contact 41 and current flows therethrough and through cross wire 75, contact H3, winding 61 of contactor S, wire 81 and contact UV2 to wire 13. Contactor S operates to close contacts S1 to S3 and open contact S4.

Controller contact 32 engages with bar contact 42 and after contact S2 closes, current flows from contact 32 through bar contact 42, contact S2, cross wire 76, winding 63 of contactor DB, contact DB3, wire 81 and contact UV2 to wire 13. Contactor DB operates to close contact DB1 and open contacts DB2 and DB3.

Current now flows through to energize the motor from wire 12 through contact L1, the circuit of armature 10, contact 22, resistor R5, contact S1 and resistor R8, all connected in parallelwith the circuit of contact 23, series field 11, winding 24, and resistor R1 and contact 1A1, and thence through resistors R9 and R10 connected in parallel with resistor R3, and through resistor R4 and contact M1 to wire 13. This increases the current fiowing through armature 10 to increase the motor speed so it lowers the load faster.

On going to the third point of lowering Lc, the operating conditions described for the second lowering point remain the same, except that contactor 3A, 4A and CR and timing contactors IT and ST become energized and contactor 1A becomes de-energized.

Controller contact 34 engages bar contact 44 and current flows therethrough and through contact L2, cross wire 78, winding 66 of timing contactor 1T, wire 82 and contact DB1 to wire 13. After the expiration of its time interval, timing contactor 1T operates to close contact 1T1 and open contact 1T2. The opening of contact 1T2 de-energizes winding 60 and contactor 1A restores to open contact 1A1 and close contact 1A2.

The closing of contacts 1A2 and 1T1 allows current to flow from controller contact 35 through bar contact 45, cross wire 79, contact 1A2, contact 1T1, winding 68 of contactor 3A, wire 82, and contact DB1 to wire 13. Contactor 3A operates to close contacts 3A1 and 3A2 and to open contact 3A3.

The closing of contact 3A2 allows current to flow from controller contact 34, through bar contact 44, contact 3A2, winding 67 of timing contactor 3T, wire 82, and contact DB1 to wire 13. After the expiration of its time interval, timing contactor 3T operates to close its contacts 3T1 and 3T2.

The closing of contact 3T2 allows current to flow from controller contact 36 through bar contact 46, cross wire 80, contact 3T2, winding 69 of contactor 4A, wire 82 and contact DB1 to wire 13. Contactor 4A operates to close contacts 4A1 and 4A2 and to open contact 4A3.

The closing of contact 4A2 allows current to fiow from controller contact 31 through bar contact 41, cross wire 75, contact H3, contact 4A2, winding 62 of contactor CR, wire 81, and contact UV2 to wire 13. Contactor CR is operated to close contact CR1 and open contacts CR2 and CR3.

Current now flows to energize the motor from wire 12 through contact L1 and the circuit of armature 10, contact 22, resistor R5, contact S1, contact 4A1 to wire 13 which is connected in parallel with the circuit of contact 23, series field 11, winding 24, resistors R1, R3 and R4, and contact M1 to wire 13. This increases the current allowed to flow through armature 10 to still further increase the motor speed and allows the lowering speed to be increased.

On going to the fourth point of lowering Ld, the operating conditions described for the third point lowering remain the same, except that contactors M and 3A become de-energized as follows.

Winding 56 becomes de-energized and contactor M restores when controller contact 27 leaves bar contact 38. Winding 68 becomes de-energized and contactor 3A restores when controller contact 35 leaves bar contact 45.

Current now flows through to energize the motor from wire 12 through contact L1, the circuit of armature 10, contact 22, resistor R5, contact S1, and the parallel connected circuit of contact 23, series field 11, winding 24, resistors R1, R3, R10, R9 and R8, and thence through contact 4A1 to wire 13. This further increases the current through armature 10 to increase the speed at which the motor drives the load downward.

On going to the fifth point of lowering Le, the operating conditions described for the fourth point lowering remain the same, except contactor 5A is de-energized as follows.

Controller contact 33 engages with bar contact 43 and current flows therethrough and through cross wire 77, contact CR1, winding 65 of timing contactor 2T, wire 82, and contact DB1 to wire 13. After the elapse of its time interval, timing contactor 2T operates to open its contact 2T1.

The opening of contact 2T1 opens the circuit energizing winding 57 and it becomes de-energized to restore contactor 5A which opens contact 5A1 and closes contact 5A2.

Current now flows to energize the motor from wire 12 through contact L1, the circuit of armature 10, cont-act 22, resistor R5, contact S1 and the parallel connected circuit of contact 23, series field 11, winding 24, resistors R1, R2, R3, R10, R9 and R8, and thence through contact 4A1 to wire 13. This increases the current flowing through armature 10 to its maximum whereby the lowering speed of the load is increased to its maximum.

When hook 17 is hoisted too high, arm 18 engages overhoist limit switch 19 causing contacts 22 and 23 to open and contacts 20 and 21 to close.

The opening of contacts 22 and 23 disconnect armature 10 and series field 11 from the source of power.

It also interrupts the power to brake winding 24 unless drum controller 25 is in the first point hoisting, Ha. The closing of contacts 20 and 21 reconnect the armature and series field in a'dynamic braking circuit which is in series with a dynamic braking resistor R11. Current now flows from armature 10 through contact 21, series field 11, resistor R11, contact 20 back to armature 10. This flow of current produces dynamic braking torque which assists in rapidly stopping the motor.

It is to be noted that relay XVR has its winding 83 connected in parallel with resistor R11 when contact 20 is closed. Relay XVR is of a special voltage type which becomes energized to operate its contact only after its winding 83 has been energized by a voltage of a preselected value, and then this preselected voltage value must be sustained for a predetermined interval of time. The time interval is set so the relay will be insensitive to normal transient circuit voltages. With relay XVR insensitive to normal transient conditions, the voltage value at which it operates its contacts may be made comparatively low. This is very desirable because it permits the setting of the friction brake almost immediately after limit switch 19 is tripped, in most all cases. Further, it keeps the speed at which hook 17 can be lowered out through limit switch 19 very slow.

When winding 83 of relay XVR is energized with a voltage of at least the preselected value and for the predetermined time interval, it operates to open its contact XVR1. Contact XVR1 is connected in series with winding 55 of contactor UV. Winding 55 then becomes de-energized to restore contactor UV and open its con tact UV1 which disconnects the power from the entire control circuit. The power source is disconnected from armature 10, which is now connected in a dynamic braking circuit of contact22, resistors R5 and R6, contact DB2, series field 11 and contact 23 by the opening of contacts H1 or L1, and M1. The power source is also disconnected from winding 24 of the friction brake so it off position, winding 55 is energized to operate contactor UV and close its contacts UV1 and UV2.

The operator may now lower the load out of overhoist limit switch 19 by moving drum controller 25 to any of the lowering positions, La through Le, it being preferred that lowering point La be used.

The motor is now energized by current flowing from wire 12 through contact L1, armature 10, contact 21, series field 11, to friction brake winding 24. Current also flows from wire 12 through contact L1, contact 20, resistor R11 to friction brake winding 24. The current then flows through winding 24 and the various resistor sections R1 through R10 depending upon the position of drum controller 25. The friction brake is thus released and the motor starts rotating to lower the load.

Should the lowering speed of the load become too great, the voltage drop across resistor R11 reaches the value at which relay XVR is operated. If this voltage is sustained for the predetermined time interval, relay XVR operates to stop further downward movement of the load by de-energizing the control circuit and setting the friction brake, as previously described.

Thus, it is seen that relay XVR not only prevents the objectionable cycling of the load in and out of the limit switch, but also prevents the load from being lowered too fast out of the limit switch.

As the load is lowered through the limit switch, contacts 20 and 21 re-open and contacts 22 and 23 reclose. This connects the motor as a shunt motor for normal lowering. The reconnection of the motor by the contacts of the limit switch could, if the load was being lowered at a very fast speed, cause a terrific jar to the craneand to the load itself. This jar is particularly dangerous on hot ladle cranes.

It is seen that relay XVR is connected across series field 11 and contact 23 during the normal hoisting and lowering operation of the hoist. Therefore, it is sensitive to any high voltage conditions that may exist across the series field. However, because of the time delay inherent in relay XVR, it is insensitive to the normal transient conditions that occur in circuits of this type.

The use of relay XVR allows the motor to be connected in the first hoisting point, Ha, as a shunt motor. This allows the hoisting speed at thispoint to be slow and smooth which is desirable.

Although we have described our invention with a certain degree of particularity, it is understood that the above disclosure has been made only by way of example, as is required by law, and that many changes in the arrangement of the circuit may be resorted to without departing from the spirit and scope of our invention as hereinafter claimed.

We claim as our invention:

1. In a control system for hoists and the like having a driving motor provided with a series field; a brake for said motor having an operating winding in series with said motor; a reversing type drum controller connected to a source by normally closed contacts of a relay, and having operable contacts and circuits controlled thereby for selectively connecting said motor to a source for rotation in either direction; a limit switch mechanism having normally closed contacts in the connections from the motor to the source and normally open contacts; a dynamic braking circuit including a resistor and the normally open limit switch contacts in the connections to the armature and the series field; a relay having a time interval after being energized before operating said normally closed relay contacts, and connected across said resistor and at least one of said normally open limit switch contacts in the dynamic braking circuit; said limit switch responsive at a predetermined limit of operation of the motor in one direction for opening the normally closed contacts and disconnect the motor from the source and for closing said normally open contacts to complete the dynamic braking circuit whereby said relay is energized, and after the time interval said relay operates to open said normally closed relay contacts and disconnect the drum controller from the source to de-energize the brake winding, and the brake sets to stop and hold the motor.

2. In a control system for hoists and the like having a driving motor provided with a series field; a brake for said motor having an operating winding in series with said motor; a reversing type drum controller connected to a source by normally closed contacts of a relay and having operable contacts and circuits controlled thereby for selectively connecting said motor to a source for rotation in either direction; a limit switch mechanism having normally closed contacts in the connections from the motor to the source and normally open contacts; a dynamic braking circuit including a resistor and the normally open contacts in the connections to the armature and the series field; a relay having a predetermined time delay after being energized before operating said normally closed relay contacts and connected across said resistor and at least one of said normally open contacts in the dynamic braking circuit; said limit switch responsive to a predetermined limit of operation of the motor in one direction for opening the normally closed contacts and disconnecting the motor from the source and for closing said normally open contacts to complete the dynamic braking circuit whereby said relay is energized, and after the time interval said relay operates to open said normally closed relay contacts and disconnect the drum controller from the source to de-energize the brake winding,

and the brake sets to stop and hold the motor; control circuits responsive to operation of said drum controller for connecting said motor to said source for rotation in the reverse direction; and said relay being connected to respond to the speed of said motor in the reverse direction and operably energized if said speed exceeds a preselected speed and after the predetermined time interval operates to open its contact and disconnect the drum controller from the source to de-energize the brake winding, and the brake sets to stop and hold the motor.

3. In a control system for hoists and the like having a driving motor provided with a series field; a brake for said motor having an operating winding in series with said motor; a reversing type drum controller connected to a source by normally closed contacts of a relay and having operable contacts and circuits controlled thereby for selectively connecting said motor to a source for rotation in either direction; one circuit including a resistor for shunting the armature and field winding of said motor to provide stable slow speed operation of said motor on a selected position of said drum controller; a limit switch mechanism having normally closed contacts in the connections from the motor to the source and normally open contacts; a dynamic braking circuit including a resistor and normally open contacts in the connections to the armature and the series field; a relay having a predetermined time delay after being energized for operating said normally closed relay contacts and connected across said resistor and at least one of said normally open contacts in the dynamic braking circuit; said limit switch responsive at a predetermined limit of operation of the motor in one direction for opening the normally closed contacts and disconnecting the motor from the source and for closing said normally open contacts to complete the dynamic braking circuit to energize said relay, and after the predetermined time interval said relay operates to open its contacts and disconnect the drum controller from the source to de-energize the brake winding, and the brake sets to stop and hold the motor.

4. In a control system for hoists and the like as described in claim 3 wherein additional circuits are responsive to operation of the drum controller for connecting said motor to said source for rotation in the reverse direction, said relay being responsive to the speed of said motor in a reverse direction and operably energized at a preselected speed and after the predetermined time interval opening the normally closed contacts to disconnect the drum controller from the source to de-energize the brake winding, and the brake sets to stop and hold the motor.

5. In a control system for hoists and the like having a driving m'otor provided with a series field; a brake for said motor having an operating winding in series with said motor; a reversing type drum controller connected to a source by normally closed contacts of a relay, and having operable contacts and circuits controlled thereby for selectively connecting said motor to a source for rotation in either direction; a limit switch mechanism having normally closed contacts in the connections from the motor and the brake to the source, and normally open contacts;

a dynamic braking circuit including a resistor and the normally open limit switch contacts in the connections to the armature and series field; a relay having a time interval after being energized before operating said normally closed relay contacts, and connected across said resistor and at least one of said normally open limit switch contacts in the dynamic braking circuit; said limit switch responsive at a predetermined limit of operation of the motor in one direction for opening the normally closed contacts and disconnecting the motor and brake from the source, and for closing said normally open contacts to complete the dynamic braking circuit whereby said relay is energized, and after the time interval said relay operates to open said normally closed relay contacts and disconnects the drum controller from the source thereby ensuring that the brake winding and motor are de-energized.

6. In a control system for hoists and the like having a driving motor provided with a field; a brake for said motor having an operating brake winding in circuit with the motor, a control circuit connected to a source by normally closed contacts of a relay and having operable contacts and branch circuits controlled thereby for selectively connecting the brake winding and said motor to a source for rotation in either direction, a limit switch mechanism having normally closed contacts in the connection from the motor to the source and normally open contacts, a dynamic braking circuit including a resistor connected in circuit with said motor by the normally open contacts, a relay having a time interval after being energized before operating said normally closed relay contacts, said relay being connected across the resistor and the normally open contacts in the dynamic braking circuit, said limit switch mechanism being responsive at a predetermined limit of operation of the motor in one direction for opening the normally closed contacts and disconnecting the motor from the source and for closing said normally open contacts to complete the dynamic braking circuit whereby said relay is energized, and after the time interval said relay operates to open said normally closed relay contacts and disconnect the control circuit from the source and de-energize the brake winding and the brake sets to stop and hold the motor.

7. The control system of claim 6 wherein said resistor and normally open contacts are connected in parallel with said series field, and said relay is connected in parallel with said normally closed contacts and said series field, whereby said relay is responsive to abnormal high voltages of a predetermined duration across the series field to disconnect the control circuit from the source.

References Cited by the Examiner UNITED STATES PATENTS 1,787,278 12/1930 Lum 318445 2,190,523 2/1940 Rogers 318368 2,308,917 1/ 1943 Hardinge 3 1 8445 2,902,635 9/1959 Kuka 318-247 X MILTON O. HIRSHFIELD, Primary Examiner. 

1. IN A CONTROL SYSTEM FOR HOISTS AND THE LIKE HAVING A DRIVING MOTOR PROVIDED WITH A SERIES FIELD; A BRAKE FOR SAID MOTOR HAING AN OPERATING WINDING INSERIES WITH SAID MOTOR; A REVERSING TYPE DRUM CONTROLLER CONNECTED TO A SOURCE BY NORMALLY CLOSED CONTACTS OF A RELAY, AND HAVING OPERABLE CONTACTS AND CIRCUITS CONTROLLED THEREBY FOR SELECTIVELY CONNECTING SAID MOTOR TO A SOURCE FOR ROTATION IN EITHER DIRECTION; A LIMIT SWITCH MECHANISM HAVING NORMALLY CLOSED CONTACTS IN THE CONNECTIONS FROM THE MOTOR TO THE SOURCE AND NORMALLY OPEN CONTACTS; A DYNAMIC BRAKING CIRCUIT INCLUDING A RESISTOR AND THE NORMALLY OPEN LIMIT SWITCH CONTACTS IN THE CONNECTIONS TO THE ARMATURE AND THE SERIES FIELD; A RELAY HAVING A TIME INTERVAL AFTER BEING ENERGIZED BEFORE OPERATING SAID NORMALLY CLOSED RELAY CONTACTS, AND CONNECTED ACROSS SAID RESISTOR AND AT LEAST ONE OF SAID NORMALLY OPEN LIMIT SWITCH CONTACTS IN THE DYNAMIC BRAKING CIRCUIT; SAID LIMIT SWITCH RESPONSIVE AT A PREDETERMINED LIMIT OF OPERATION OF THE MOTOR IN ONE DIRECTION FOR OPENING THE NORMALLY CLOSED CONTACTS AND DISCONNECT THE MOTOR FROM THE SOURCE AND FOR CLOSING SAID NORMALLY OPEN CONTACTS TO COMPLETE THE DYUNAMIC BRAKING CIRCUIT WHEREBY SAID RELAY IS ENERGIZED, AND AFTER THE TIME INTERVAL SAID RELAY OPERATES TO OPEN SAID NORMALLY CLOSED RELAY CONTACTS AND DISCONNECT THE DRUM CONTROLLER FROOM THE SOURCE TO DE-ENERGIZE THE BRAKE WINDING, AND THE BRAKE SETS TO STOP AND HOLD THE MOTOR. 